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Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow?
This question is related to the answer I found on this particular thread, about the Frames in a Turbofan.
In a turbofan what holds the spinning axis?
I went on this thread after some research on Google, since recently I started working in the industry. I'm working on this particular part of the frame, and I would like to understand more about it. Also I am currently working on understanding more about jet engines in general and how they work, I find this absolutly fascinating since I found a lot of information and answers to my questions - and now for the curiosity :)
My question is about the Fan Frame here (GE CF6/CFM56 Turbofan on pics)
I would like to know the use of the 12 Circular Holes on the inside of the frame, between the 2 flows (Low-pressure compressor way, Right?), you can see here what i'm talking about on those pictures (Red arrows).
(I don't think this is to make the part lighter, because the outside edges of thoses holes, are re-inforced a lot with a big extra thickness.)

Thank you.

A very nice first question! Welcome to Aviation Stack Exchange. If you haven’t already, can I suggest taking the tour and reading the [help] so you can learn how this site works and continue contributing quality material like this.

Short answer
These holes are vents used to discharge air from the primary (core/hot) flow into the secondary (bypass/cold) flow. They are normally closed by valves (variable bleed valves, VBV). The valves open to maintain the compressor pressure/flow within a safe area.
VBV in operation: Youtube

VBV on a CFM56-5 (also visible the VSV). Source
VBV are a mean to prevent a compressor stall in turbo-engines. A  stall appears in situation like this:

For some reason, e.g. when thrust is reduced, pressure at the compressor exit exceeds by a large amount its inlet pressure.
When the pressure ratio is beyond the compressor capability, air at the exit starts opposing compressor airflow, a reverse pressure wave is created, which propagates to the inlet.
Flow over one or more compressor blades is disturbed and the airfoil stall angle is reached creating an aerodynamic stall.
The stall is extended to the next blades, i.e. a rotating stall develops.
The pressure ratio is getting unstable.
Thrust is suddenly reduced, attempts to increase thrust accelerate the stall.

The VBV are used to adjust the compressor pressure ratio, by discharging some air between the LPC and the HPC. This decreases both the pressure ratio of the LPC and HPC and helps preventing compressor stalls.
Holes location
The fan frame assembly shown here without its outer shroud:

Fan frame assembly, without its outer shroud, of a CFM56-7B. Source
comprises two rings of 12 stationary vanes which are crossed by:

The primary (core/hot) flow for the inner vanes
The secondary (bypass/cold) flow for the outer vanes.

The 12 holes/vents in the mid-box structure of the fan frame assembly are closed by 12 variable bleed valves (VBV):

VBV in a CFM56-5A. Source
The valves are protected by a grille:

Source
Location of these elements in the engine:

Location of the fan frame in a CFM56-5. Source
Details:

VBV on a CFM56-5. Source: CFM56-5 Training Manual
The master valve is controlled directly by a motor, the other valves are linked to the master VSV by a flexible shaft.

5: Fuel gear motor powered by HMU, controls position of the master VBV
1: Master VBV
2: Position feedback
4: Position sensor
7: Flexible shaft controlling the other valves

VBV use
As regard to the cold flow, the inner duct is located between the low pressure compressor (aka booster) and the high pressure compressor. The pressure delivered by the compressor section is optimized for maximum engine power.
When the engine speed is low or the engine is decelerated, the LP compressor pressure can increase and clear the LP compressor stall margin. In such a case, the VBV are opened to release some air into the secondary flow and restore the margin. Conversely, when thrust is increased, the risk of stall disappears, the valve is closed to restore efficiency. The following diagram shows how the action on the valve contributes to keep the compressor flow in the designed working area.

Stall prevention using VBV. Source
More on VBV and stall prevention:

What is the difference between variable and transient bleed valves?
How does the FADEC prevent compressor stall during rapidly increasing thrust demand?

VBV for debris rejection
On military aircraft, unsuccessful attempts have been made to use VBV to capture and reject debris and water. The principle is to create a bend in the airflow with an opening at the start of the bent section. Heavier elements are captured by the hole. CFMI has reintroduced this technique in the LEAP engine.

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text:
Throughout aviation history, what airships were metal clad?
Throughout aviation history, what airships were built with metal skin instead of fabric or other material?

There was a wooden airship. Everyone was very excited about it, but it wooden fly.

@Richard: If I were you I wooden tell that joke anymore.

@FredLarson - I should leaf now before I tell acorny joke.

@Richard: I saw what you did there, and it really goes against the grain. But I think your bark is worse than your bite.

@FredLarson - We should stop this now before the moderators take a fence.

@Richard: Agreed, because Stack Exchange hates fun. But thanks anyway!

At least two all-metal airships are known to have existed, the first one invented by David Schwarz, and test-flown in Tempelhof, in 1897. It flew, but crashed when landing.
Another one, a really successful and better known aircraft, was an American airship, the ZMC-2, that first flew in 1929.
https://en.wikipedia.org/wiki/David_Schwarz_(aviation_inventor)
https://en.wikipedia.org/wiki/ZMC-2

There was no stipulation on whether the airship had to carry anybody. This Myth Buster experiment successfully flew a very large LEAD balloon (30-50ft dia).

There is a metal airship currently being built by an Englishman in France, called the VariaLift. https://www.varialift.com/

The specifications are as follows:

Welcome to Aviation! While this may theoretically answer the question, it would be preferable to include the essential parts of the answer here and provide the link for reference. Maybe you could include an image and a couple more details about it?

"metal airship currently being built by an Englishman". While it was expected the first prototype should have been ready last summer, it seems they are still building the hangar.

It doesnt need a hangar. If youre looking at photos of a hangar shaped structure - thats the airship frame - the build it outdoors in sections on a production line. Theres no hangar, just assembly sheds and they are old WW2 buildings which are still in place.

source: Stack Exchange

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What experimental techniques should one employ during cruise flight to determine correct airspeed to fly for max range in a headwind or tailwind?
Theory demonstrates that one ought to increase speed in an headwind, and decrease speed in a tailwind to achieve maximum range.  A lengthy discussion on the theoretical solution was answered, though not clearly, here.  It is unlikely that a pilot will have the Thrust Required chart on which to draw a tangent line through the x-axis intercept at the given wind speed.
What simple techniques should the pilot employ to determine the best speed to fly given specific environmental conditions (fixed headwind or tailwind)?

Max range is basically how long you can stay in the air at the fastest airspeed. Your optimum range, regardless of headwind, will be to set your airspeed for your economy cruise setting at that altitude. Speeding up in a headwind will just increase your fuel burn and probably reduce your range.

Not true.  There is a tradeoff between speeding up to spend less time in the headwind and the increase in fuel burn.  There is a theoretical speed that should be flown in a headwind. It is the point of the curve tangent to a line that intersects the x-axis at the negative of the headwind.

This is tough.  Have you researched the Carson speed?

The discussion given as reference by the OP is quite comprehensive. Using the polar of your own plane, you can tabulate at home the best range speeds for different wind conditions, and have them handy in the cockpit...

@acpilot I had not researched Carson speed, but I found this paper: "Fuel Efficiency of Small Aircraft." http://cafe.foundation/v2/pdf_tech/MPG.engines/AIAA.1980.1847.B.H.Carson.pdf

what kind of instruments do you have, do you know your groundspeed? Do you know your fuel-consumption?

@rul30 Yes to Fuel Flow and GS. Also, IAS, TAS, SAT, derived wind speed, and most other "standard" instruments.

An old technique is "Half the Headwind, all the Tailwind".
So if you're flying into a headwind of 20kts, increase your cruise speed by 10kts. If it's a 20kt tailwind, decrease your Cruise Speed by 20kts (but only as far as BestEnduranceSpeed).

I like the stickiness of that technique. Where did you hear/learn it?

It's an old Ferry Flight / Coastal Command technique, ie it goes back YEARS . Ina headwind you need to punch into the wind, but if you increase speed too much you'll burn much more fuel as the drag curve rises. So a ballpark Half-The-Headwind is a simple compromise. If you want anything more accurate than that, then you'll need tables of Weight v FuelFlow v Airspeed, and a few hours of calculating Groundspeeds and MilesPerGallon with differing winds.

In a good day, with no wind, you can make trial glides and note down the values of the variometer and of the anemometer. Four or five points are enough to draw a best-fit parabola. Once you have it, you find the best range speed for any wind condition by tracing a tangent to the parabola that starts at the value of the wind. You note down the airspeed given by the tangent, and that's the best range speed for that wind condition. You may make a list of winds and the corresponding best range speeds and have that list handy at the cockpit.

Do you have an example of this?  I'll try it out.

@acpilot  Here's an example curve with tangents, taken from the reference given by the OP: [img]https://i.imgur.com/wXgl4hZ.jpg[/img]

How do you determine thes placement tof the tangent?

While the technique may work, it describes an exhaustive method that is impractical.  First, on a good day, there is NEVER "no wind." Second, the range of altitudes and airspeeds for a high performance aircraft makes this simple method an enormous undertaking.  Variometers are useful on gliders, but they are not as accurate on most other aircraft.

@Mark Jones Jr.  Well, a good day, 'with no wind', is desirable because of the lack of turbulence, that makes measurements easier. In itself, the wind has no influence on them, as the plane flies always within the mass of air, moving or not. That doesn't matter for polar-drawing...  It's true that airplane instruments aren't exceedingly accurate, but they are enough for practical purposes, as is the case here... And the method isn't 'an enormous undertaking'. I have drawn those curves many times...

Best Endurance
Vg
plus headwind component
OR minus tailwind component
Or Carson Number
(Cost = 16% increase in fuel consumption)
Carson = Vg x 0.32
Headwind = Carson + (Headwind/3)
Tailwind = Carson - (Headwind/3)

Most of what I've read suggest Carson's Number is only good for small aircraft and not high performance aircraft. Have you heard differently?


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When did the color orange enter flight test?
When did the color orange enter flight test?  As early as the Bell X-1, pictured here, aircraft were painted orange to enhance visibility. Later, in 1959, a study was conducted that suggested the utility of orange markings on aircraft.  In 1968, the Society of Flight Test Engineers adopted a logo with "flight test orange" as its color.

There are, however, few references that explain the following:

When orange flight test equipment (wires, parts, LRUs, etc.) first appeared.  For example, I transcribed a 1977 article from the SFTE's Flight Test News that sets 1949, anecdotally, as the time/event that caused Douglas to use orange wire. But it also references a Mil Spec. (Does anyone know more about the Mil Spec referred to?
When orange flight suits first appeared?
When aircraft (in general) adopted orange paint schemes for flight test aircraft, as seen here?

related

@PhotoScientist I too have heard of this spec, but I too have not found a copy.  However, my understanding it that specifies colors and their makeup but not their application. Does it say, "use orange wire"? Or does it say "use this shade or orange when orange is needed for aviation?"

Here's an 50's era jet in NASA service but the color looks to be more red than orange.  https://www.nasa.gov/centers/armstrong/history/where_are_they_now/F5D_802.html

Thanks quiet flyer

They were originally used to allow ground spotters to better spot the aircraft from the ground for optical tracking during flight test.  Another use of painting wingtips, tailplanes and tailfins bright colors was to allow observers a better means to determine the aircraft’s orientation and attitude in flight.
Finally if it all went so wrong so fast, hi viz colors made it easier for SAR crews to locate the wreckage....and the remains of the pilot.....quickly.
I know the Navy and the USMC were using orange flight suits as early as the Korean War, not for their test pilots, but for fleet air crews to make it easier for SAR aircraft to locate then in the event of a ditching or bailout over open water.

There nothing wrong with your edits.  I guess I just like the grimmer reality of mine.

This is true for the aircraft, but they found the color did not work well.  However, it does not answer "when" or whether the X-1 was the first.

+1. A side note about ditching in the ocean: A common anecdote among scuba divers is about the "yum, yum, yellow" referring to the bright yellow, orange and red used in maritime stuff to attract the attention of sharks. That's the reason most scuba vests are dark

Authoritative answers may no longer be possible.
Even the best-informed collection of experts on this, the
Flight Test Safety Committee,
only a few years ago reported in an article
"A Brief History of Flight Test Orange" that (Q. 1)

The origin of this color tradition is largely unknown

and that (Q. 2)

bright orange flight suits are also a common sight, but the emergence of this fashion statement is also of unknown origin.

Also for Q.1, that newsletter's next article, "Where did the (Orange) Wire Come From?", mentions a

Mil Spec requiring all flight test wiring, brackets, etc., to be orange

without quoting a number.  But that article might be just another transcription of your 1977 one.

Thanks. I wrote those articles.

How embarrassing!  It never occurred to me to compare stackexchange names with the newsletter's real-world names.

When aircraft (in general) adopted orange paint schemes for flight test aircraft, as seen here?

Never. Orange was used for a few aircraft only (X-1 is the most famous example), so it was never "generally adopted". In fact I have a hard time finding any other orange aircraft.
This happened right after the X-1:
X-2: white
X-3: white
X-4: white
X-5: white
An image search for "flight test aircraft" shows a sea of white and unpainted metal, with only a couple of orange ones in between.

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text:
How important is it to have talent to become airline pilot?
The situation that led me to ask the question is as follows:
I am a student pilot with only about 10 hours of flight time. I passed the aptitude and personality tests prepared by German Aerospace Center (German: Deutsches Zentrum für Luft- und Raumfahrt).
My instructor keeps on telling me since the very first couple of flights that I lack some talent and it's not really possible for me to become an airline pilot. (He has never flown as airliner, only military aircraft but he is obviously a good pilot with long teaching experience.)
So, what is the possibility that he is right? How much and what type of talent is required?
Please note that I haven't caused any major safety problems, and other students claim that they made pretty much the same mistakes I do.
Edit : Since some people misunderstood the situation, I'll clear some issues:
1-) I'm on some scholarship program of an airlines company. Money isn't an issue.
2-) I'm generally considered to be pretty smart.
3-) There's no reason that I could be discriminated by the instructor.

You might consider switching flight instructors, this particular flight instructor just might not like you for some particular reason.  Personal biases can play havoc with their ability to be impartial when assessing skills.  Granted, if you go through 3 or 4 instructors and they all say the same thing...  But just one instructor does not make a valid sample size.

From what you've said here, the only conclusion I can draw is that the instructor lacks talent.  To say you lack talent, and then not follow that up with a precise, actionable, positive criticism of exactly what that means, where the gap is and how to close that gap would be enough for me to sack my instructor.  You're paying the bills!

You don't disclose much personal information (besides that you are in Germany), however, could it be that for some reason the instruction believes people like you shouldn't become pilots? Are you someone who he could be biased against? Like being female, foreigner, another race? In any case, find objective criteria to determine how good you are.

Your instructor is an asshole. Find a new one.

Giving so much respect to an instructor who openly demoralizes you itself reflects your talent..

@anshabhi With all due respect, I cannot agree that the giving of respect publicly (which this forum is) is a reflection of talent. Here's why: When I was young, and I'm assuming taco is since he is a student pilot, I was reflecting my upbringing by respecting those with greater experience than I.

Somebody once told me that and it turns out that I looked like the guy who his wife cheated with.  Sometimes, it's just not you...but the world.

By all means, do try a different instructor. But, sometimes it IS you. There is something called a "feel for flying" and I think most instructors would tell you that some people have it more than others. Some people can learn to coordinate stick, rudder, and throttle much faster than others. Some can correct mistakes easily once they're pointed out, while others keep practicing the wrong thing over and over. etc. The same is true in performance driving and many other fields.

The above pretty much sum it up. Find a new CFI. An example, when I was teaching, I had a student who got airsick on our first 4 lessons. It was the only time I've ever had to keep barf bags handy, and I actually considered telling him he might want to find something else to do. I'm glad I didn't. He stuck with it, and honestly became one of my best students. He finished Pvt quickly and sailed through Instrument rating. I kept him through most of his Commercial rating before I left. As far as I know, he is an airline pilot today.

If your question is answered, you can mark the one as the accepted answer.

You are asking the wrong question. Ask yourself this:
Do I really want to become a pilot?
If the answer is yes, then you can become a pilot. You only require hard work, and a lot of money (but we are not talking about this).
Having talent is subjective. Sometimes you try to learn something new and you get into that relatively quickly. Sometimes you don't. It doesn't just depend on talent, but on several factors.
If you feel that you are not making any different mistakes than other student pilots, then change your instructor.
There are several discussions about changing flight instructors. You can benefit from these ones:

What to look for in a flight instructor?
Is there a downside to trying multiple flight instructors?

Thank you for the answer. I don't have reputation to upvote but I'd do if I can.

@tacoburrito You'll have it soon.

Rather than asking yourself "Do I really want to become a pilot?", ask yourself "Do I really want to fly?" It's a subtle but important difference; don't let yourself be dazzled by the lifestyle aspects of being a pilot, focus on the core activity.

@GhillieDhu In the case of an airline pilot, I think the lifestyle aspects are very important to consider, also (and these may vary depending on your location.) Salary (or lack thereof for at least several years,) being away frequently, and other such factors are also important to consider before committing years of training (and likely lots of money) to the career.

I attended USAF pilot training, attracted by the idea of "being a pilot"; it took over a year for it to sink in that I didn't actually enjoy the act of flying. YMMV.

Telling the student what they want to hear.

A bit of talent surely helps, but most important is the ability to learn and show progress.
A friend of mine had to do six simulator tests before he was admitted to the flight academy of his choice. Each one was a little bit more complicated than the previous one. After five tests he had perfectly demonstrated to lack any talent and they were about to fail him. They told him that he could do the final test if he insisted but that it would probably make little difference.
He flew the final session flawlessly which demonstrated that he was a very good performer under high pressure. So they let him pass. Unfortunately a few months later he didn't pass a medical test due to unforeseen conditions.
So talent isn't really needed, however it surely helps. As Farhan says, with hard work and lot's of money and good health you can become an airline pilot.
The question is whether you really want to spend that money and effort on a job that provides little security in today's market?

This is a bit off topic but you should do yourself a favour and look into the disputes between Lufthansa and their pilots, how Ryanair hires its crew, into the way Middle East airlines employ their pilots, what pay-to-fly schemes are, etc. Becoming an airline pilot today does not mean you will get the same working conditions as those who became airline pilots 40 years ago.

I like that you presented the ugly truth along with the beautiful dream.

The sad reality is that airline pilots are highly skilled, highly trained, often endure extremely difficult working conditions and have responsibility with "consequence of error" far higher than 99% of all other professions but yet, are often treated little better than bus drivers.  All in the name of demand for low cost and bean counters who cannot equate quality with quantity.

Like anything, a combination of talent and effort is usually required to become proficient and/or master a complex skill. The less talent you have, the more work you need to get to the same level as someone with more innate talent.
Your instructor is probably adopting the mindset that the commercial airlines get to pick the best of the best, so they will choose new recruits that show a very high aptitude for flight in general and commercial flight training specifically. The same applies to military flight schools like the one your instructor would have gone through; there's usually a hundred applications for every opening, so the recruiters are told to weed out anyone who's not absolutely perfect for the job.
However, let's draw a parallel. If you were to judge a student driver's lifetime aptitude for driving a motor vehicle from the first 10 hours of time you spent in the passenger's seat with them, and that judgment carried any weight for a career doing it, there would be no professional drivers in the United States. Forget it. Insurance companies in the U.S. don't even back off the "teen driver" insurance rate until you're 25; if you got your license at 16 that's 9 years of being considered "high risk" just because of your experience level.
Back to aircraft, you can't even get your commercial pilot's license in the U.S. until you've logged at least 250 hours yoke time (as a PPL holder with at least 50 hours logged already and flying two hours a week for fun, it will take you up to four years to log that much time), and you can't even show your face on a commercial airliner as First Officer until you've logged 1,500 total flight hours, then you have to log another thousand hours minimum as First Officer to fly an airliner as Captain. And those are the absolute minimums, assuming you don't log any flight time that doesn't also directly contribute to another requirement of your commercial license such as cross-country, instrument approaches etc; a PPL can log a thousand hours and not meet the other requirements for a CPL, and most pilots double the minimum logged hours while meeting these other requirements. So, talent or not, if you haven't killed yourself or gotten your license pulled after almost three thousand hours at the controls of an airplane, you know what you're doing and you've likely seen it all.
Back to you and your instructor, I concur that it's probably not a good fit; your instructor is inspecting too much too soon (ten hours is really not even enough to accrue the necessary training for a solo endorsement), and I'd look around for another instructor with a little more patience for you to have some "aha" moments about flying.

Regarding the driver's license comparison, I would note that part of that is specifically the 'teen' part, rather than the 'experience' part. If you start driving at 25, you don't get the teen rates. While the experience part is a factor, just the fact that the people involved are teenagers (and, as such, statistically much more likely to do stupid stuff) also plays a large role in the risk factor.

True, but you can also get a student's pilot license at 16 and the minimum age for a commercial is just 18, so the potential for teenagers at the yoke is there if they or their parents have the money for the plane, fuel and instructor. The point remains that whether you're 16 or 36, if you have a total of ten hours' actual driving experience you won't be impressing an instructor or examiner.

I assume your flying instructor does not work for the airline, and is not responsible for their hiring processes.
If that is true, then I wouldn't worry about it. You're not applying to be a military guy like him and you won't need his particular set of skills - we hope. :)
Finally - much more experienced pilots have said you shouldn't have to rely on your superior flying skills.  What you really need is superior judgement, to avoid needing such skills...  I guess they know what they're talking about.

To put this slightly differently - military pilots of certain aircraft definitely need to have a different type of skill than airline pilots, and I know several people who are experienced civilians who haven't made the cut in the military. Maybe he doesn't see that particular skillset in you, @tacoburito, but that doesn't mean you can't be a successful (And safe) airline or private pilot. I'd think about switching flight instructors

Everybody has his own learning path. A good instructor adapts to the way each student "works". Even if not, you'll just need more time before you learn how to learn with him. I believe, anyone can be taught to become a pilot, eventually.
However, not everyone will make a good pilot. Please keep in mind, that after you've made your license you'll have to compete for the seat in the cockpit. If you are competing against more talented people you are in a weak position.
It can be a hard decision, but you must take it if you don't want your dreams crash disastrously after a few years of hard work (and quite a bunch of money, too). The best way, I believe, is first get your PPL, then ask few friends/instructors to honestly rate your flying skills. Continue towards the ATPL only if they rate you higher than 60%. Otherwise, my honest advice is that you stop there and keep your PPL. After all, it's an amazing hobby!
I wish you to make through your training soon. Success!

Talent is important, so is luck, and so is having decent instruction but in my opinion, most important is having the right attitude. That means when things are not going as you expect, taking positive action to change them.
Your instructor says you don't have talent. Fair enough, maybe they are right, maybe not. Coming here to ask if it is important isn't really addressing the issue though since you still don't know what it is your instructor is talking about and that means you still do not know what action you need to take to change your instructors opinion. You respect your instructor, which is a good thing, but do not grant them authority they do not have or make assumptions without evidence

he is obviously a good pilot...

then why is he teaching beginners and why don't they know what he is talking about?

then why is he teaching beginers -- I know quite a few excellent pilots who are lousy instructors (often because they'd rather be doing something other than instructing). One skill does not automatically confer the other… .

then why is he teaching beginers isn't really relevant in this case. I know excellent pilots who teach students of all levels (including beginners) simply because they want to transfer their knowledge to the next generation. Teaching beginners is in no way the sign of a lack of skill.

But how many of those excellent pilots have students that don't know what the pilot is talking about? My point was not to degrade pilots that teach beginers, it was to degrade teachers that only teach beginers and still struiggle to be understood.

Please tell your instructor from myself, another flight instructor, that he is, to put it delicately, completely full of sh*t.
Here's the thing about flying an aircraft.  It encompasses a wide range of skills and abilities which will highlight your strengths and weaknesses as a human being.  A student pilot may be quite skilled with flying, say, steep turns, but then struggle with ground reference maneuvers or instrument flight.  What you have to do is simply persevere; if you are weak on a certain skill, you need to practice it more until you are good at it.
And some people are naturally gifted at certain things and lousy at other ones.  Itzhak Perlman is gifted at playing a violin, Tom Brady is a gifted football quarterback, and Bob Hoover and Chuck Yeager were (are!) gifted pilots.  Just because you can't play a violin or chuck a pigskin or fly an airplane like those guys doesn't mean you can do any of those activities for pleasure or for profit.  You might even be quite good at them, too.  But some are more naturally talented than others.
Second as my scathing remark at the beginning of this post might suggest I have a major problem with a lot of people out there doing flight instruction and the general state of flight instruction today.  Most are just building hours until they can get a better paying pilot job or are terrible teachers with little interest in their students.  This hurts aviation tremendously.
Keep in mind as well that the fact that someone was once a military pilot does not mean a high degree of skill or proficiency.  There are plenty of mediocre or unskilled military pilots out there.  Even some fighter pilots are lousy aviators.  Its true.
There is also a tendency among some - often ex-military aviators - to take a 'holier than thou' attitude towards civilian pilots and instruct in a manner similar to the mean neighborhood kid who wanted you to feel intimidated when trying out his new 10 speed bicycle.  My general opinion of such people is with poor regard; he's abusing students to stroke his own ego.  If I have a CFI working for me and find out he's doing that kind of crap with a student, he'll be fired faster than you can say 'pink slip'.  Scroll back ten or so years to their training in the military, they were the same people in a T-6 or T-38 crying like a little punk while some hard nosed IP berated them for every mistake they made.  They never learn that this sort of crap is a mark of a poor educator, let alone a human being.
All that aside, I'd have to see what it is that you are struggling with to learn.  There are only three cases where I would terminate training a student; struggling to learn some skills isn't one of them.  If you have the time and commitment to learning to fly, you can do it.  It's that simple.
And like any other pilot certificate or rating you get, these are just journeyman's licenses to practice airmanship.  Flying takes a lifetime to master; there are people with tens of thousands of hours of flight time who go up and learn something new on each flight.
Don't quit, don't suck, don't be an a**hole.  And fly good.

Maybe you should change your instructor! If the second instructor agrees with the first one then you need to work really hard on the areas they are highlighting.
I am not a professional airline pilot but I am an enthusiast and have flown big jet full motion simulators both airliners and fighters. The hardest aircraft you will fly are small light aircraft in general and particularly IFR, when you are getting tossed around in a bumpy cloud, on your own, with nobody to help you but yourself and its taking you half of your concentration just to keep the wings level. The larger ones are easier.
I would say that your attitude and your approach to your work and your decision making, your ability to think and stay calm, etc etc. is more important than this thing you call "talent". Some people appear to be born with "talent" which just means they pick things up quicker, but this is nothing that hard work cannot replace. You have just got to want it enough and put enough effort in. Good luck!

That is a polite way of saying you are not smart enough. You are not alone. For the majority of people who try to fly the same exact thing happens as happened to you. The instructor can tell in the first 5 minutes if a student can "make it", meaning they have the intelligence and coordination to learn to fly a plane. If they are sub-par, then the first flight just becomes a "ride" and when the aircraft gets on the ground the instructor gently breaks the news to the student somehow. In your case he tells you, you "lack talent". Each instructor has his own way of doing it.
Flying an aircraft is HARD. Things happen simultaneously in 3 dimensions with 6 degrees of freedom. You have to be a certain intelligence level to do it, which is about 130-135 IQ. If a person is below this level, it is very dangerous for them to fly and they have a high probability of making an error that will kill them and possibly other people. There is no shame in not being a genius. Every person needs to know and respect their limitations.
You are you lucky you had a good instructor. There are unscrupulous instructors out there who will string a non-candidate along, taking their money even though they know the student can never be soloed. This is greedy and dangerous, because they keep taking dangerous students up in the air. It sounds like your instructor has been taking you up multiple times, however, and he really shouldn't be doing this.
Flying is fun and a great dimension to life, but for most people, unfortunately, they need to do it from the passenger's seat. There are a lot of ways to enjoy flying without being a pilot. I encourage you to explore those other options.

Comment on some of the other answers: Some of the other answerers, who are obviously not CFIs, have said things to the effect that "anybody can fly if they want to hard enough." This is both a factually wrong idea and expresses a dangerous and delusional attitude. An aircraft is not like a car that just runs into a ditch when you screw up. An aircraft WILL kill anybody who is not fully competent and tries to fly, and I know of several such people who have killed themselves in that way. CFIs do not tell unqualified students not to fly because they are jerks. They tell them that to save their money and maybe their life. Listen to them.

Do you have any sources to cite for your claim that pilots with lower intelligence are in much higher danger?

My flight instructor's certificate  says : AIRPLANE SINGLE AND MULTIENGINE and INSTRUMENT AIRPLANE, and I spent 2000 hours exercising that privilege. During my career I was for a time the chief flight instructor at the flight school that, compliments of the GI bill, trained more pilots than any other school in my state. With all due respect, I have to say that what I observed, both about students and instructors, does not match up with your answer. In particular, I often saw new instructors make the mistake of believing they could evaluate students in the first 5 minutes.

Driving a standard transmission is HARD. You need to judge the engine's power band by feel and ear. When starting from a stop or on a hill you need to finesse the clutch in order to get the vehicle moving without an uncomfortable lurch. On hills you need to worry about stalling the engine or rolling back into cars. Once moving you must manage the engine's power band while steering and navigating. Some people will never develop the skills necessary to do this, but those who do will almost universally take more than "the first couple of drives" to learn to do it well enough to pass a road test.

I am not a CFI. Every CFI I have ever talked to has said that it is usually immediately obvious when a student will not make it. I realize my answer is "unpopular" and that the average person loves the "anybody can fly" idea. My experience is that that is not only untrue, but the promulgation of that idea results in needless deaths. I think encouraging non-soloable students to keep trying despite indications that they lack the intelligence to fly is foolish, gives false hopes, wastes money and sometimes results in avoidable deaths of both students and instructors.

@TylerDurden It's true that not everyone can be taught to fly, just like not everyone can learn to drive a standard transmission, but it's also true that a good chunk of students don't "click" with their first instructor for one reason or another, and that changing instructors can often overcome a learning obstacle. If a student wants to learn but is just "not getting it" I think they owe it to themselves to try a different CFI before just giving up, and I think a good CFI would encourage them to do so, or at least offer more actionable feedback than "you lack talent" (like "Do X, not Y.")

@TylerDurden I'm confused by your "needless deaths" theory.  The CFI is always at the controls and can take over the aircraft at any given moment.  The CFI will not let the craft get into a situation in which they cannot recover from, and if they do...well, it's not really the students fault, is it?

And as far as "wasting money" it's the students money to waste.  If they love flying, perhaps it is not a waste to them.

@JayCarr That is what the unscrupulous CFIs tell themselves: I can always protect against an error, so it is ok for me to baby sit this incompetent and collect their money. That is exactly the way they think. The error in this should be obvious to even a non-pilot: that works until some unusual situation crops up where the student's blunder ends up being uncorrectable or causes a problem that happens so fast the CFI cannot react in time.

@JayCarr Concerning money, its not just a matter of the student losing money. Its that a fraud  is occurring the bad instructor giving the student the impression that they are making progress toward a license when the instructor knows he will never be able to solo the student. That's fraud.

@TylerDurden - I think you said it best: "I am not a CFI." And until you have been either that, or at the very least some sort of teacher, you don't really have the scope to make the claims that you have, especially about someone's intelligence. If you've talked to a bunch of CFIs who claim pilot skill is quickly obvious, then they really don't know what they're talking about. True pilot skill can take a while to assess properly.

@TylerDurden - Your basic assumption of me being not intelligent enough is dead wrong. Besides, in case you don't know, test of DLR covers that area by evaluating mental skills of a person from different angles.
Also, how can they be qualified enough to evaluate a student in 5 minutes? That is a ridiculous claim. People may agree if you say 10 hours, but 5minutes? No.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Do the FACs compute every speed value shown on the PFD speed scale, or only stall speed and maximum speed?
On an Airbus aircraft, the Flight Augmentation Computers (FACs) control the rudder and have windshear detection, and the FACs also are responsible for speed computations. I know the FACs continuosly compute stall speed and compute the maximum speed but do the FACs also compute every other speed on the speed scale; VLS, alpha protection, alpha floor, green dot speed, flap retraction, etc., so basically the FACs compute every speed on the speed scale?

Do you have an idea of where the numbers would come from if they were not all computed?  Knowing that would help us to understand what you are asking.

@WayneConrad They can come from the FMS. In the A320 architecture, the FAC computes characteristic speeds based solely on sensor inputs like AOA, trim, altitude, fuel level. The FMS computes the same with the addition of user-input data like ZFW/CG. The FMS speeds are more accurate but are subject to user error. Which is actually displayed on the PFD depends on the model and generation of aircraft.

Yes. Kind of--the air data computers do some of the computations and display those based on hard coded limits.  For example, an ADC will compute current AOA and may have the AOA limits hard coded therein.
The air data computers also provide input to the FACs, which further limit the aircraft speed envelope based on altitude, speed, and configuration.  The FACs are necessary for configuration information and flight control positions.
A detailed explanation of the what the FACs accomplish is here.
There is a related question.
Other examples of ADCs and their respective displays appear here and here.  The first shows mechanical systems which compute a normalized AOA based, and later in the same article, a Gulfstream display shows feathers for Max AOA on the ADI, as seen here.

So the FACs get all their information from the ADC and the FACs compute all the data they get and display it? Could you give me another example of an ADC computation and display?

Answer edited to include other examples of AOA displays.

I dont understand what you mean when you say the AOA has hard coded limits? Doesn't AOA limits depend on altitude, weather, speed, configuration, and so on?

No, Max AOA is the same regardless of speed, altitude, bank angle, etc.  An airfoil will always stall at the same AOA.


text:
Why are airports like Roswell and Fresno so popular for flight tests?
I recently visited Roswell, NM, and was surprised at how many flight tests have been performed there.  Even the fatal Gulfstream flight test crash happened there. My research shows that a lot of flight tests happen at places like San Bernardino, Roswell, Fresno, and  Moses Lake. My research turned up only simplistic explanations for why these airports are so popular like "Boeing chose the San Bernardino facility because of three factors: hangar size, availability and weather." (Source: The Sun News)  Is that really all they consider in determining flight test locations?
I've heard that you can't do flight tests at just any airport, though I haven't been able to find any relevant legal restrictions.  The airport choice doesn't even seem to be just the obvious factors like weather, runway length, and GA availability.  (I also don't care about specialized testing that would require unusual airports like long runways or specific temperatures.) There are a few dozen low-volume long runways in the arid American West and similar regions.  Why are just a few so popular?  Are there any FAA (or EASA) restrictions on doing flight tests at any old airport?

Do you want it broken down by type of test activity -- i.e. post-maintenance, customer acceptance, production test, type certification, experimental?

I'm mostly interested in the certification and development testing, like brake testing for certification or "let's see if the avionics for approaches are actually working correctly" tests.

@CodyP Would like to see a reference for "Fresno," as I have never heard it was a popular location for flight test in my many years of flight test professional experience.

You can do flight tests from almost any airport, but it helps if:

The weather is dry and stable,
the field is not too far from the factory,
there is a large unpopulated area nearby, and
you have support facilities available.

The support facilities were installed by the Air Force, and the other factors were already taken care of by Mother Nature in the case of places like Fresno or Roswell. Given that the distance from Los Angeles, a major aviation industry hub, to Fresno is only a bit more than 200 miles, flight testing in predictable weather and over the open terrain west of Fresno becomes very attractive. If you look at Lancaster, the next town near the vast Edwards Air Force base, the driving distance to Los Angeles is only 70 miles. This should help to explain why Edwards is today the main Air Force test base. Once you have a long runway and some experienced flight test engineers in place, other manufacturers will also converge on this location in order to make their flight testing more predictable and effective.

Most of this seems to be correct, but proximity isn't always a driving factor.  Roswell isn't close at all to Gulfstream or Boeing HQ, or really anything that's not military.  Even Fresno doesn't seem like an obvious choice based purely on proximity to LA and nearby unpopulated desert considering all the alternatives like Palmdale, Palm Springs, Bakersfield, Edwards/Mojave, and even Yuma.

I do wonder about Fresno and weather, though.  In winter, the San Joaquin Valley tule fogs often reduces visibility to near zero.  In summer, dust and smog make it less than unlimited.

The FAA does regulate "where" flight test can be performed, in 14 CFR Part 91, which says:

§91.305 Flight test areas.
No person may flight test an aircraft except over open water, or sparsely populated areas, having light air traffic.

Application of this rule differs depending on the stage of flight test. The FAA also provides guidance on how to extrapolate takeoff data in Advisory Circular 23-8C.  In particular:

When the basic takeoff tests are accomplished between sea level and approximately 3,000 feet, the maximum allowable extrapolation limits are 6,000 feet above and 3,000 feet below the test field elevation.

Therefore the elevation of the field at which testing is performed matters a great deal. In addition to the length of the runway and stable weather conditions, the elevation of Roswell, NM (~3,500 feet) allows for a greater range of extrapolation than an airport closer to sea level.

For a couple of your specific examples:
Roswell is specifically chosen for braking performance tests because it is one of the few remaining >10,000 foot long ungrooved runways in the US. Braking performance testing requires ungrooved pavement for the wet runway data.
Moses Lake is the closest (relatively) low traffic airport with a long runway to the Boeing factories, and the weather in eastern Washington is generally better than west of the mountains (especially in winter), making it a convenient choice for tests.
San Bernardino (and Victorville) are lower traffic airports in Southern California with facilities for a transport category aircraft. Southern California tends to have better weather than Seattle in the winter, so some tests get moved down there depending on time of year. They provide access to the restricted airspace at Edwards (R-2508) and off the coast (W-291). A lot of the test flights out of KSBD head out over the water.


text:
Are there any serious plans for a new supersonic civilian aircraft?
Since the retirement of the Concorde and the Tupolev Tu-144, there aren't any civilian airplanes (passengers carrier or business jet) flying supersonic. I heard that Dassault and SAAB had rather advanced studies on this topic but abandoned them due to various problems.
Does anyone have current references indicating that an aircraft manufacturer plans to develop a supersonic transport aircraft?

I think this will be a difficult question to answer. First, it's highly speculative and unless you work for a manufacturer it's unlikely you can say anything for sure (and even then your employer might limit what you can say publicy). Second, it's also subjective because one man's "serious plan" is another's "daydream". It might make for a great discussion, but it can't be answered 'correctly' in my opinion.

I agree that it is probably OT, but it is a question that we're likely to see often.  I wonder how best to restructure these questions

I don't think this is primarily opinion based (serious may be subject to opinion, but I think most people would agree on what is not serious), and while I question whether it's answerable, I think it's a legitimate question to ask, and I don't see the harm. Maybe the answer right now is "No", and maybe down the road someone will identify a "Yes".

I'm not sure about "primarily opinion based" but this question is asking for information that seems "way to rapidly changing" -- Even if we use well-sourced information to formulate an answer, if we're not going to then keep the list of "serious plans" up to date our answer will be obsolete in a few months/years. Which ones got built? Which died on the drawing board? What new designs popped up? etc...

Here's another one: BBC: Spike Aerospace S-512 supersonic jet - expected 2018

Aerion is planning a supersonic business jet which has a projected completion year of 2021:

Here's an article Forbes have written about it.


text:
Why aren't we using drone blimp/hybird airship for delivery?
Currently, the heaviest weight a commercial drone (the type that delivers Amazon package, not the type that delivers tons of stuff) can lift is 4.5kg with a 30-45 minute battery life. A drone blimp/hybird airship might be bigger and slower, but it would take less energy--the lift is generated by the balloon or some lifting surface instead of the propellers. Since the Boeing 747 win against the Concorde because it can carry more people with a cheaper price despite much slower than Concorde, why aren't we using a drone blimp/hybird airship to deliver Amazon packages instead?

Delivery of what? You're going to have a blimp deliver Amazon packages?

Yes, I am thinking about Amazon packages or even Uber Eats

What size is this drone blimp? And, where will it land? How will you get the package from the drone blimp to behind the concrete pillar at my front door? Are you planning on airdropping a package into my backyard? What about pools? Am I going to have to install some sort of package receptacle or landing pad? Who is paying for that? Will it go with my landscaping? What about the nearby high tension power transmission lines? How will that work with the 400’ altitude limit? What about the line-of-sight rules for Part 107? Will they be able to operate above people walking by on the sidewalk?

How much wind can your blimps (or FTM your drones) handle?  Hereabouts, in some seasons 30-40 mph or more is a normal afternoon breeze: http://www.twainquotes.com/Zephyr.html  A good winter storm can bring much higher winds, enough to flip semi trailers.

@user39178 you should precise in the description the kind of packages you want to deliver. pizza delivering (constrained by time, your pizza has to be delivered less than half an hour after its baking and hardly weight the 4.5km limit of your example) is not the same as books, clothes or electronic material (weight, density, cargo value). Remember that the 747 was a good choice for hub-and-spoke model, hardly what a food deliver drone network would look like.

Also it might looks like a dupe, I think this question can be slightly transformed to avoid being a dupe. The market is clearly not the same. It is about small legs delivery (from the warehouse, the airport or a restaurant to any point in the same city, typical deliveroo's market) whereas the potential dupe address longer legs, from airport to airport or from airport to huge industrial site.

@Manu H: Also, a lot of package delivery isn't within cities, it's from delivery company's freight terminal to some suburban or rural location that's many miles/km distant.  It would be highly inefficient to send out drones/blimps carrying one package at a time, instead of a truck that drives a route to deliver all packages.

There are many reasons why that will probably not happen.
Number 1: As of right now drones/blimps are very big for 1 package. It is much more efficient to use a car that can take in hundreds of packages.
Number 2: There are may types of drones/blimps that can be flammable exposed to certain chemicals. Also... where is the drone going to fly? In airspace where planes are? Where is it going to land? What about apartment buildings?
That's why this is not plausible. Maybe one day it will be.


text:
What effect do urban wind conditions have on operating tiltwing aircraft and gyrocopters?
From this research it seems there are quite a lot of strong wind in suburb residential area and around high-rise buildings. High-rise buildings would also create wind tunnel effect and eddy winds.
When trying to land or takeoff in heliports, or rooftop helicopter pads, would the wind cause the tilt wing or tilt rotor aircraft to flip or move around? Would the wind big enough that when the wing rotated 90 degree, the wind could push the aircraft away from the desire landing spot?
If it is a gyrocopter, would the rush of city wind, or even the eddy wind, drive the top rotor harder so the landing or takeoff becomes an issue?

A tiltrotor in landing configuration is for all practical purposes a normal helicopter with two relatively inefficient rotors.

A gyrocopter might be able to land on a rooftop helipad if you time the flare just right (due to lack of collective it is no longer controllable when it stops moving forward, making it difficult), but it needs runway to take off, so no take-off from helipad.

It isn't totally clear to me what you are asking.  Do you think the effects of wind on tilt rotor or gyrocopters is different than it is on traditional helicopters?


text:
What characteristic my canard needs to have when the canard also carries a pair of engine?
I am in 3rd year Aerospace Engineering and trying to do a preliminary design of an airplane. My design has a front wing that also has an engine at its root on both side of the fuselage.

There is another engine with thrust vectoring nozzle at the back of the aircraft. The canard is a low-wing set up and the main wing is a high-wing setup. Of course, they can all change. At VTOL takeoff and landing, the front wing would rotate 90 degrees so the engine could point downward. During cruise the engine would rotate back to be horizontal. Since the canard could fully rotate, and it also carries and thrust component, I just don't think it fits the definition of the different canard types as described in the wiki. Since the rotation of the front wing could change the direction of 2/3 of the aircraft's thrust, there is no need to have any camber in its airfoil, right? And the only requirement of this wing section's aspect ratio is that its wing need to be stubby so there won't be much drag and countertorque when the front wing is rotating?
Edit: maybe I have made a wrong assumption, I should not arbitrarily set all of the engine to be the same thrust. I should set that these two engine at the front provides a thrust that is reasonable, that could ensure the balance of the aircraft during VTOL.

It's making lift and providing pitch control when it's horizontal isn't it?  Why would you want an uncambered airfoil?

You say that a rotating "canard" controls 2/3 of the aircraft thrust. To maintain balance that would require the fore wing to develop 2/3 of the lift, meaning that it is not a canard but the main wing. Can you clarify what you mean here?

I am not sure whether this canard should be a control canard, lift canard, or stabilizing canard. Also, by "2/3 of thrust" I mean since two out of three engine in the aircraft is fixed to the canard, when rotating the canard, the direction of thrust would be rotate too

@user39178: the aircraft must be balanced both in vertical take-off and in hover, so if you have 2/3 of the vertical thrust there, they can't be that far forward, which means they don't have much leverage to provide control. Also either the main wing is quite close to the canards, which probably won't be very efficient, or the canards are carrying significant lift (assuming the third engine is near the tail, not on the other wing, so the canards don't need to produce 2/3 of lift).

maybe I have made a wrong assumption, I should not arbitrarily set all of the engine to be the same thrust. I should set that these two engine at the front provides a thrust that is reasonable, that could ensure the balance of the aircraft during VTOL.


text:
What counts as the wingspan of a tandem-wing aircraft?
When calculating the wing-span of a tandem-wing aircraft, like the QAC Quickie Q2, which set of wings do we use for that value? There are two sets of wings, and they both provide lift. In the class, they just teach me that b is for wingspan, but they didn't go into detail about non-conventional aircraft. I am using that value to calculate the wetted aspect ratio of my aircraft

Maybe it depends on what you're using the value for?  Estimating lift area, buying a hangar door, ...

I am using that value to calculate the wetted aspect ratio of an aircraft

Because wetted aspect ratio $b^2/{S_w}$ merely improves on wing aspect ratio as an estimate of efficiency, for $b$ just choose whichever wingspan is largest.  That's good enough to compare one tandem planform to another.
You could get fancy and use a weighted average of the wings' spans, weighted by how much lift each one produces, with those in turn weighted by time spent in climb, cruise, and descent... but that seems against the spirit of a quick estimate provided by two easily measured numbers.


text:
The cost of these aircrafts in modern US dollar?
Could you tell me where I can find the development cost and market price of a Fairey Rotodyne, Convair CV-240, Martin 4-0-4, Ka-22 in current US dollar?

find the contemporary cost 2) use an inflation calculation https://www.usinflationcalculator.com/ 3) profit!

The problems is that there are a lot of technical data of those aircraft, but not much financial data


text:
Why would sea level static thrust have a takeoff and a maximum continuous value?
In the type certificate data sheet for a jet engine, there is this table
static thrust is the thrust generated by the engine when the plane is at rest with respect to the Earth and the surrounding air. So why would it have different values? And is the plane still "at rest" at these values?
Also, what is the different between thrust and sea level static thrust here?

It is from http://aerodesign.stanford.edu/aircraftdesign/propulsion/tvshv.html

The static thrust value is with the engine fixed in place in still air.  Imagine the engine on an outdoor test stand, or on an airplane with the brakes on or tied down.  As soon as the airplane starts to move, the thrust value declines and the static thrust value no longer applies.  The static thrust value at sea level is used because it provides a consistent baseline reference, because once the engine starts to move, additional variables come into play.
The lower chart is showing the relative decline in thrust with speed for the range of engines between pure jet (bypass ratio = 0) to very high bypass (5-6), to illustrate the impact of bypass ratio on the decline in thrust with speed.  "Static thrust" is implied at the speed value of 0 Mach (airspeed is zero, so you are "Static" by definition) as a value of 1 and declines in thrust from static are a value less than 1. So you can interpret the left edge of the chart as "static thrust" and everything to the right as (moving) thrust, with the curves going down and recovering (or not) with increasing Mach #.
It's just illustrating relative effects, so with 6 engines that have different bypass ratios, their decline with speed, from the engine's Sea Level Static Thrust (whatever it is, represented by the value of 1), is shown by each curve. Following the curves as an example, the pure jet has only lost about 7% of its rated static thrust with speed at Mach 0.5, whereas the very high bypass fan has lost over 40% of its static thrust value at Mach 0.5, in the same atmospheric conditions.

the name is called "take off (5 minutes)" because take off requires more thrust than cruise?

So is the sea level static thrust in the graph representing the "take off (5 minute)" value or the "maximum continuous" value?

Yes takeoff thrust is always more than max continuous because takeoff requires the most performance. I would assume any value quoted as static thrust is a takeoff thrust value, since the static condition, operationally, represents the beginning of the TO roll.  To get decent takeoff performance, the engine maker is granting permission you might say, to flog the engine much harder than normal as long as that is limited to 5 min, and not reduce the engine's minimum life expectancy. You will however maximize life by reducing the max thrust where possible, which is where "flex thrust" comes in.

Turbofans use a gas turbine core to drive the low pressure fan which produces most of the thrust by moving large volumes of air. This requires large amounts of torque which the low pressure turbine extracts from the hot exhaust gases exiting the gas turbine's core.
To develop more power you burn more fuel which means more heat. Low pressure gas turbine blades are usually rated over 2000F meaning they will melt if exposed to too much heat.
The reason for the rated 5 minutes of thrust is simply because the turbine blades will overheat causing premature wear and possibly engine failure. To produce the rated thrust the turbofan is at sea level in stationary air hence the term "static".
As the forward airspeed increases and the density of the air reduces due to increased altitude the rated thrust will go down which is not represented in the chart.

so even though the term contains "static", the aircraft is still moving forward at take off speed?

The aircraft is not moving in a static test.

but is the engine fixed to the ground or the thrust value is just the maximum thrust it could produce without the plane started moving?

It's the maximum thrust developed in a test where the engine was fixed (probably on a test stand) with given power levels.  "take-off" in the first chart refers to the power setting, not to the motion of the engine.

in the graph above, is the sea level static thrust the "take off (5 minute)" value or the "maximum continuous" value

@user39178, as the heading over the table shows shows, both sets are "sea level static thrust".    The difference in the two sets is what power is selected.  You get more thrust when you push the levers forward.


text:
Is there a way for the helicopter rotor to get its power half by wind, half by engine?
Imagine a gyroplane, if something happen mid-flight (when the plane is basically an autogyro and the engine provides no power to the helicopter rotor) and just the wind generated by forward flight can no longer turn the helicopter rotor enough to provide enough lift, could the engine partially take over? Like using the engine to provide just enough power, with the rest provided by the wind, so the helicopter rotor could spin enough?
I don't want the plane to autorotate downward. I want the plane to keep flying, but using the engine to increase the rpm. If the incoming wind could turn the top rotor in a certain rpm, could we increase the rpm using the engine? In my memory, rotodyne could do this because it uses a tip jet, but what if we use normal piston or turbine engine?

Are you talking about in a hover, or very low forward speed such that you can't auto rotate? I suppose you could come up with some kind of clutching mechanism, but I'm interested in why auto rotate isn't an option?

What would happen other than the engine dying?

The problem is that as an autogyro, the air is going through the rotor from below, and as a helicopter, the air is coming from above and it has to be one or the other.
In any case, gyroplanes don't have a problem of low rotor rpm as long as you keep the rotor loaded (and you always keep the rotor loaded).  If you slow down, the rotor rpm doesn't decay, the machine just descends steeper.   You can slow a gyro to zero airspeed, and it will maintain most of the rotor rpm on its own and autorotate straight down, although the vertical speed may get pretty high. If you have a landing gear that can tolerate a 500 fpm descent, and start from only 20-30 feet or so, you can land like that.  This is why some small autogyros don't even bother with a rotor rpm gauge.
So to get low rotor rpm, you'd have to unload it to take away the aerodynamic forces driving the blades around by pitching over to go zero G or close to it, and at that point an engine might be useful to keep the rpm from dropping, but you'll have probably already chopped the tail off from the blades flapping down (low G maneuvers in gyros are to be avoided at all costs - as with 2 blade helicopters, for different reasons), and you'll already be on your vertical trip to your final resting place anyway.

It's true that the rotor spins at a more or less constant angular velocity at normal flight airspeeds, but if the forward speed falls to zero and the machine enters a vertical autorotation, the rotor revs fall by about 10%... In the classic gyros of the 1920s and 30s, you could autorotate to the ground, vertically, and survive the landing, but modern gyroplanes can reach 1500 fpm in vertical autorotation, and that's too much...

Why not just talk about autorotation with helicopters.  Don't they fully disengage the drive and "glide" down to land?  In that case the wind can turn the rotor.

But the wind has to reverse direction through the rotor when the helicopter turns into a gyro glider.  You regulate rpm n a helicopter gliding with collective pitch changes.  His question is about auto gyros anyway.

@xxavier I don't think you watched the video linked. The vertical sink rate is somewhere in the range of 500 fpm.

@John K It's a very light machine, the 'Monarch'; and those vertical drops are from 15-20 meters or so only. The gyro hasn't enough altitude to accelerate, in vertical autorotation, to the very high terminal speed it would reach. At a prudent altitude, I myself have experimented vertical autorotations with the prop at idle in a conventional gyro (ELA-115) and got scared (and recovered) when the sink speed passed the 1000 fpm mark... I've written those 1500 fpm 'off the top'. I'm not sure now, but I think it's the calculated terminal speed, for a gyro of 400 kg and a rotor dia. of 9 m...

What do you mean by "load"? Also, I don't mean autorotating downward, I mean the engine is still running, and I am trying to compensate the amount of lift that the propeller cannot produce by just turning by the wind. By increasing rpm with the engine, the lift should increase, right?

@xxavier ok fair enough.  I'll make some edits.

@user39178 Load refers to maintaining  more or less 1G flight, as opposed to going partially or fully ballistic by pushing over. When you unload the rotor so it's no longer doing much lifting, the RPM will quickly decay.When flying forward in a gyro, the rotor is tilted back so the air is striking the disc from below in level flight and as long as the air is coming that way, the rpm is maintained. In a helicopter in forward flight the disc is tilted forward and the air is striking the disc from above.The point is there isn't a need for what you are suggesting if you fly the machine properly.

Most present-day gyros have a two-blade teetering rotor that has to be kept always under load, since it is the airflow associated with that load what keeps the rotor spinning and the blades rigid. If –as happens with zero-G maneuvers– the rotor revs fall below a certain value, the blades lose their 'centrifugal rigidity', and they may flap out of control, chopping the tail and the propeller. It has happened more than once.
It could be interesting to have a direct mechanical connection between the engine and the rotor, so that it could be kept revving above the critical level even at zero load. With a degree of forward airspeed, the torque reaction can be contained with the rudder. That 'partial rotor power' has been tried in a few experimental machines gyroplanes in order to attain shorter takeoff runs.

No, the rotor's power is (in flight) never "by engine."  Whenever such an aircraft is not touching the ground, its rotor is fully in what helicopterists would call autorotation.
Gyroplane, autogyro, and gyrocopter mean the same thing, depending on what part of the world you're in.  In flight the rotor is unpowered.  It may be powered before takeoff for convenience, but not in flight.  The engine provides only forward thrust, through a conventional propeller, not through the rotor.


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Why do airlines outsource regional flying?
The three major American airlines (American, United, and Delta) all have regional brands. These brands are actually operated by other airlines (ie: SkyWest). Air Canada has a similar regional brand called Air Canada Express.
Obviously, these flights are important for getting passengers to the airline's hubs. It also seems obvious that this type of flying is quite profitable because there are a number of regional airlines that are flying for these carriers. Why don't the big airlines just fly these routes themselves? Why have they all chosen the path of outsourcing?

This article breaks it down super nicely, and has most of the info you are looking for. The key quote from my reading of it is

The simple answer is that using regional airlines saves major airlines
  money compared to them operating a flight themselves. Where do the
  cost savings come from? For one, employees are paid significantly
  less.

There are also some serious union and historical reasons for the setup, regional airlines code sharing with majors is in some regards a way to skirt around union negotiations

The first reason is that it would likely eliminate the cost advantage.
  Most major carriers have negotiated with their unions that flights
  with fewer than “X” number of seats will be operated by regional
  airlines. You can bet that if the regional airlines became part of the
  major airline (even if a separate division), the major carriers’
  unions would be fighting for significantly better pay for those crews.
...
Historically another reason the major carriers have contracted out to
  regional carriers is because it allows them to share some risk. Keep
  in mind that historically airlines are ridiculously unprofitable
  (though that has changed recently). So leased planes were almost a
  liability rather than an asset, given that they were losing money with
  just about each flight.

Here is another interesting paper on the subject and good info here.

Sorry for this late response, but thanks for the answer. I never considered this angle.


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What is the proper procedure when a passenger seat belt becomes inoperable during flight?
I was on a Delta flight in Business class on a 777 and during flight the motor of the seat caused the seat belt buckle to pop off the end of the seat belt causing the seat belt to be inoperable.
This was a completely full flight and the flight attendants were unable to fix the seat belt.  I ended up just tying the two ends of the seat belt together for landing and the crew found that acceptable.
What should the proper procedure be in this case?

You are quite a risk taker.  What if there was an emergency evacuation upon arrival? How fast could you undo that knot?  Were there no empty seats on the airplane?

I agree, this was not ideal but when I realized the buckle was gone we were already on final approach and there wasn't a single seat available according to the crew.   That's why I'm wondering what the crew should have done in this case.

I find it interesting that they didn't have any spare seat belts available. We used to carry spares in case of breakage, but this was back in the 1990s and there weren't any power seats, at least not on the 747s I flew.

Re the close votes: I think this question is on-topic here. Surely it is on the passenger side of things, but it is about aviation regulation, safety and evacuation procedures etc.

If there is an answer to this, it's probably in Delta's crew manuals, I don't think there's any regulation or FAA guidance that's specific enough to address it. Perhaps you're really asking "why didn't a crew member give up their seat to keep a passenger safe?"?

@Pondlife -- I suspect most scheduled air carriers (FAR 121 or equivalent) would be reasonably similar though, so another carrier's policy might be indicative at least...

I'm going back to ATOMATOFLAMES and S is for seat belts. I would be surprised if the MEL for the 777 doesn't include seat belts. I don't think the flight was legal with the non-functioning seat belt if they couldn't find an alternative seat for you. I believe you can sue them for endangering your life :)

@PrashantSaraswat it was functional at takeoff.

@Terry Looking at photos, it appears that Delta uses airbag seatbelts in their herringbone business, so it may not be possible to swap them in flight like the traditional style.

The flight crew should have given you a seatbelt extension to fix the connection. And if that did not work, then you should have been instructed to hold on and ask other passengers to hold you down for landing.
Also, if you were wondering why the flight attendant did not move you to an empty the jump seat, is because FAA regulations don’t permit.

Don't seat belt extensions work by attaching to the fixed seat belt? If the buckle is no longer attached to the belt, there wouldn't be anything to fit the extension onto.

That's correct a seat belt extender would not work in this case since the buckle was completely missing.

You wrote in a comment:

I agree, this was not ideal but when I realized the buckle was gone we were already on final approach and there wasn't a single seat available according to the crew. That's why I'm wondering what the crew should have done in this case.

I suspect they could have put you in a crew jump seat in the back of the plane, there's almost always one un-occupied.

You might be right, but this doesn't seem to answer the question about whether there's an official procedure for use in this situation.


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How does the "pendulum effect" affect biplanes?
A high wing airplane will correct itself (lateral stability) when disturbed because its c.g. is below the c.p. (looking at the plane from its side), according to this forum post and the book below.
So my question is, how does this "pendulum effect" affect a biplane with two centres of lift?

I must note that at the end of that forum discussion somebody (totally not Peter in an alternate timeline) also makes the point Peter explains in his answer: there is no such thing as pendulum stability, its a misconception

See Rocket pendulum fallacy. And here’s a good demonstration using a drone: https://youtube.com/watch?v=OYHCP3-mpxk

Disturbed - but how? A fixed wing aeroplane in a stationary, zero sideslip turn is roll neutral. There is no tendency from gravity to upright the roll. Not for a monoplane. Not for a biplane. Not for any number of fixed wings.

The last picture in the OP with the vertical lift vector for the rolled aircraft is wrong: the lift vector deflects with the wing and is always perpendicular to it, therefore always points though the CoG. The picture only considers the stabilising moment of the vertical component $L_v$. and conveniently disregards opposite moment of the horizontal lift component $L_h$, which magically counteracts the rolling effect of the vertical component.
Disturbed in sideslip caused by $L_h$: yes, this causes an aerodynamic rolling moment, from several mechanisms.

Wing/fuselage interference
The high wing aeroplane tends to upright itself due to the usual sideslip direction in a turn, a low wing wants to increase the bank angle.

Wing dihedral or V-shape. Velocity w in the aeroplane Z-axis when the wing is not perfectly aligned with the airflow.

Wing sweep. The sideways velocity of the sideslip causes different relative velocities over the two wing halves.

Please explain how a hang glider turns.  Displacement of lift and center of gravity will create a rolling motion.  A side slip must have significant velocity for purely aerodynamic effects to "right" the aircraft.  What you propose essentially is an aircraft that must constantly "Dutch Roll" to remain upright. Obviously, this is not a practical mechanism for passenger transportation (although it is theoretically possible). Please review aircraft design.

@RobertDiGiovanni a hang glider turns by pointing the lift vector sideways, like all aircraft do when they do a banked turn.

Bingo!  And how is that wing rolled sideways??? "Pendulum" is a bit more palatable considering the case of weight ABOVE the wing (destabilizes roll). Dihedral and lower CG are roll stabilizers, sweep and high CG create "Dutch Roll".  Shifting CG away from Lift Center (hang glider), or shifting Lift Center away from CG (ailerons), will create roll.

@Robert Assuming a roll to the left, the wing is rolled sideways because the left rolling moment created by the right wing is greater than the right rolling moment created by the left wing. Gravity has nothing to do with it; the only effect gravity has on an aircraft is on its linear velocity.

@RobertDiGiovanni Yes correct, a hang glider has a wing that can hinge - a hinged wing, not a fixed wing. It can mis-align lift from the CoG. Please note that I'm not proposing using Dutch rolling to control the aircraft, that is what the flight controls are for. A fixed wing has no direct static stability derivative for roll angle, only indirect via sideslip. Dutch roll is a dynamic response in two degrees of freedom.

So why is the caption "anhedral wing in sideslip" attached to an illustration of a dihedral wing?

@quietflyer. Oops, lost in translation, thx.

@RobertDiGiovanni: A hang glider does not shift the weight, it shifts the wing. Weight shifting is impossible due to the conservation of momentum.

It will affect a biplane just as much as a monoplane.
Not at all.
The pendulum effect does not exist in airplanes. It does in airships, but not in heavier than air craft.
For a proper discussion, we should first define what a pendulum is. Only then can be established if such an effect can exist in airplanes.
Let's base the definition on Wikipedia. It says that

A pendulum is a weight suspended from a pivot so that it can swing freely.

Maybe it is also worth to look closer what a pivot is: A thing on which something turns.
So the pendulum is fixed to a fulcrum which keeps it suspended and allows it to swing freely. The ideal pendulum has all its mass in its massive bob and, therefore, pivot and center of gravity are not in the same place. If the center of gravity and the pivot would fall together, a pendulum could only rotate but not swing. And that swinging motion is what the pendulum is all about.
Now for airplanes: Here we have no pivot. All rotation can only happen around the center of gravity. This is equivalent to the pendulum with no length which is no pendulum any more.
Lift is the sum of all pressure acting perpendicular to the direction of movement. Lift on a banked wing will also bank with it. The lift vector will still be in the plane of symmetry of the banked aircraft and will have no lever arm with the center of gravity, thus causing no uprighting rolling moment. The Figure 34 of your copied book page is simply wrong. The author did not know what he was talking about.
Edit especially for @JohnK:
I added an answer here about the rolling maneuver of paragliders. The description should make obvious that no pendulum effect is involved. Rather, the whole is quite similar to roll control in hang gliders where the lift is shifted sideways in order to create an imbalance, but then again different in wonderful ways. The discussion below would not allow me to explain my thoughts in such detail.

Comments are not for extended discussion; this conversation has been moved to chat.

But, as long as we are consulting Wikipedia, see this page.  This is what I mean when I talk about "pendulum effect".  Note the importance of sideslip.  Yes, it is a bit of misnomer, but it's come to be a widely-used term.  To me the term "keel effect" is just as problematic as "pendulum effect" or more so, because it gives the impression that there is a parallel to the way that buoyancy exerts an upward force at the center of buoyancy, high above the CG (which is low due to the heavy keel weight), creating a righting force even without sideslip.  https://en.wikipedia.org/wiki/Keel_effect

An important point is that even if true sideforce is minimal, drag can still create a roll torque during sideslip, if it acts well above or well below the CG.

Pendulum effect is a bit of a misnomer.  What is thought of as "pendulum effect" is actually just a favourable rolling moment that can be generated during sideslip if the center of mass is a large distance from the lateral aerodynamic center, which doesn't really exist on normal aircraft.
Paragliders however,  which operate in a kind of topsy turvy alternate world of control, exploit this effect to achieve lateral stability and to turn.  A paraglider turns by skidding, the skid being created by increasing the lift and drag on the into-turn side when you pull the trailing edge down with brake application (you are only interested in the drag increase, not the lift increase, which is working against you - you are only interested in the lift increase when using both brakes together to slow down and flare).
Doing this (applying brake on one side to turn that way) actually creates a small aerodynamic rolling moment in the opposite direction of the turn (like trying to turn an airplane to the right by lowering the right flap and aileron only - doesn't work so well in that case), but because the center of mass is more or less down where the pilot is, and the lateral aerodynamic center is up by the wing someplace, the lateral force on the pilot to the outside of the skid massively overpowers the differential lift created by the brake application and rolls the glider to the right.  And you can say that it's sort of acting like a pendulum, kind of.
You could say that paragliders exploit this effect to use adverse yaw to turn the wrong way, allowing control with inputs that are seemingly opposite to the normal world (turning right by lowering right aileron as it were).
As well, the mass way below the wing creates a strong centering effect (you're basically hanging from a parachute that is able to glide forward) and if spontaneous sideslip occurs the restorative rolling moment is immediate.  It's also how paragliders are to somehow magically be able to achieve very strong yaw stability without any weathervaning element like a fin or sweep. Yaw and roll are strongly interconnected due to the mass 15 feet below.
So you could say that there is a pendulum effect but it only works for paragliders, or maybe some crazy airplane with most of its mass in a concentrated bob weight at the bottom of a long rigid pole extending below it, with most of its surface area at the top.  In any normal airplane, the lateral aerodynamic center and the center of mass are too close together for this effect to overpower the other forces and are insignificant if they exist at all.

Please rethink the last paragraph. The paraglider first creates a lift and drag difference between both wingtips which pulls the wing sideways and starts a yawing rotation. This rotation in combination with the now offset pilot mass will increase the bank angle. The question, however, is about how a bank angle can create a counteracting rolling motion without pilot input. This is quite different from how a paraglider turns.

Peter and John, I will not insist on butting in on your conversation too much, but please consider the paraglider - it turns by wing warping! This works because the Pendulum prevents it from rolling into the other direction! The wing (and pilot) will yaw in the direction of the increased drag.  Now a bird will have another trick up its sleeve, it will fold up its inside wing to roll into the turn (instead of ailerons), then use its tail to yaw (a slip turn).  This is more like air craft do.

If you are turning a paraglider and remove the brake input, adverse yaw created by the brake application stops and the glider starts to fly straight. Being banked with the yaw removed, it starts to sideslip toward the low side.  The mass below the side slipping wing rolls the glider level, or at least level after several overshoot oscillations if you just let it go, depending on the glider. Some gliders are very well damped in roll and immediately return to wings level, some oscillate and get get into rolling PIOs if counteracting brake inputs are ill timed and end up feeding the oscillation.


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What does "Independent visual approach" mean, at airports with parallel runways?
I have read that some airports, with parallel runways, use this procedure - INDEPENDENT VISUAL APPROACHES, but I could not understand very well the meaning, and for this reason, the purpose. Please, can you help me?

Consider an airport with only one runway. In order to keep aircraft safely apart (and to give them time to exit the runway), all aircraft must be separated by some distance as they are on final approach.
RWY 27  ————— *   *   * <-- acft 3NM in trail

If an airport has two parallel runways, now you can have aircraft landing on both of them. But if the runways are too close together you need to worry not just about spacing in line to each runway on its own—you also need to worry about spacing side-to-side with aircraft approaching the other runway. You may have to have dependent approaches where the position of an aircraft on final to one runway determines the position of an aircraft on final to the other. For example, you may need to ensure that aircraft are staggered on the finals with one mile of diagonal separation:
RWY 27R ————— *   *   * <-- acft 3NM in trail
               \ / \ /  <-- 1NM diagonal separation
RWY 27L —————   *   *

But if the runways are far enough apart, or if you have the correct procedures in place, you can run independent approaches. That means each aircraft on final is only a factor for the aircraft also on the same final—they can be side-to-side with aircraft on the parallel final.
RWY 27R ————— *   *   * <-- acft 3NM in trail

RWY 27L ————— *   *   *

This concept can apply to instrument approaches and/or visual approaches depending on how the local aviation authority has set out its rules.

Heartwarming to see that ascii art remains alive and well.

@randomhead: Thanks a million!


text:
How does the GMU44 magnetometer differ from a magnetic compass?
In comments to Is the Garmin G1000's heading indicator based on a Magnetic compass?, it's claimed that the GMU44 magnetometer is not a magnetic compass.
I don't understand this claim, as the device is a magnetometer, which senses the Earth's magnetic field, meaning it's aligned to the magnetic poles rather than geographic poles¹, and it will be affected by local magnetic anomalies (unless stabilised using gyro correction).
Is there some definition of "magnetic compass" that excludes such magnetometers, and if so, how are they categorised?

¹ possibly with corrections in the processor, just as you have offset adjustment with a mechanical compass

The GMU44 is a magnetic compass. Any device that measures the direction of earth's magnetic field is called compass, including electric ones. There's also the term magnetometer, which is a device that measures the strength of a magnetic field. A multi-axis magnetometer measures strength and direction, which means you can use it in both roles. In the G1000, the GMU44 is used in the compass role.
That said, the heading display in a G1000 is primarily a gyroscopic instrument, but slaved to a magnetic compass (the GMU44) to prevent heading drift.

Do you have a source for your last statement? I think you are definitly right but never found a description of this.

As I explained in my previous answer, the magnetometer can detect its orientation in the Earth’s magnetic field by measuring the electrical signals from the pickup coils in a flux gate.  A magnetic compass makes use of a bar magnet, generally suspended in a liquid such as kerosene, and attached to a card which is referenced to a fixed lubber line on the casing of the compass.  The bar magnet swings freely, and so naturally aligns itself with the magnetic field of the earth.  A user can reference the compass card in reference to the lubber line and deduce magnetic heading based on this.
Magnetic compasses should not be confused with a gyro compass or a heading indicator.  These are independent units which maintain a preset zeroed indication using a gyroscope and must be periodically aligned with a reference, such as a magnetic compass, to compensate for accumulated deviations due to gyroscopic precession.
Of the two, a magnetometer is a little more precise, and that it is not subject to lead/lag or compass swing errors during turning and acceleration and less affected by magnetic deviation as the flux gate can be placed well away from electronic equipment.  Conversely, a magnetic compass does not require electric power to operate.
And technically speaking, a magnetometer isn’t even a compass at all. It’s just a piece of equipment used by an integrated flight deck or conventional HSI (which are also NOT magnetic compasses) to provide directional orientation with magnetic north.

You've just describe the difference between a mechanical and electronic compass - which are both magnetic compasses (unlike the gyro unit, which is not).

Think you need to go back and re-read the definition of what a compass is.

A compass is a thing that tells you what direction is "north".  Doesn't matter if it uses a gyroscope, coiled wires, or a cart with cleverly-designed gearing.


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Can regular emergency exits not work after crashlanding?
Live accounts of survivors of Bangla Air 211 mention getting out after breaking windows but not out of the emergency exits.
My question is can regular airline exits not work in such cases?

As a rule of thumb, if you see more than one copy of something that serve the same function in a system, that thing is usually known to the designer of the system to fail more often than they really want.

@user3528438 You're suggesting that there being more than one emergency exit means that emergency exits fail too often? It has a heck of a lot to do with needing to get a lot of people out the plane quickly, and that means multiple doors.

@DavidRicherby And also with crashes tending to result in situations where some exits may be particularly undesirable places to leave the aircraft (e.g. a fire, running jet engine, or fuel spill on one side or a water landing where the back of the aircraft is submerged.) There's a reason that the certification requirements require that the passengers have to be evacuated in the test using only half of the doors (and exactly which ones those will be are not told to them ahead of time.)

@user3528438 your rule of thumb is sorely misguided.

@Federico How so? Weight is of critical importance on an airplane, designers would never put extra redundancy if necessary safety and reliability requirements could be met with less. Why engines went from 4 to 3 to 2...

@user3528438 There are other reasons to make multiple copies of something.  For instance, many planes have more than one wheel on each landing gear, but the rationale is not due to the failure rate of wheels.  It's for weight distribution.  I think that if you amended your rule of thumb to include the word "redundant," it would be more likely true.

"Working" is a delicate conspiracy against entropy, no matter what you are talking about.  It is always possible for anything to not work, especially after you smash it into something else.

All regular exits are generally used in an emergency. This information would be included on the safety card and in the briefing by the crew before the flight.
Of course, during a crash, structure can deform and exits can become blocked. Regulations require evacuation within time limits using only half of the available exits. This must be demonstrated to be possible.
Here is a Q400 safety card, showing that two forward and two aft exits are used for evacuation. The forward right exit (called R1) is an emergency exit.

Source

Note the instructions on that safety card to look out the exit's window first and not to use it if you see fire or debris in the way.

Well the short answer is, it depends. As already noted in a comment, an aircraft’s structural integrity can be jeapordized in the event of a crash landing. This primarily comes down to the impact itself. How powerful was it? What forces acted upon impact? Did these forces impact the emergency exit or its frame? Emergency exits, just like any part of an aircraft, are not indestructible; even a block box can be severely damaged due to some impacts for that matter. With that said, let’s say the aircraft in this scenario has 6 emergency exits. If the first three do not open after a crash landing, it doesn’t necessarily mean the other three won’t. Think of it similarly to a car accident. Whether or not the doors open after the impact relies solely on whether or not the door itself, the door jam, or the mechanism opening the door were damaged enough for it to not open due to the force of the crash and whether or not those forces acted upon any of these factors. Like an aircraft, just because the driver door in a car doesn’t open in a particular accident doesn’t mean the passenger door won’t and vice versa.